1. Field of the Invention
The present invention relates to an error correcting device and an error correcting method. More specifically, the present invention relates to an error correcting device and an error correcting method that correct erroneous data included in data read out from a nonvolatile memory.
2. Description of the Related Art
Semiconductor elements such as flash memories, which store information depending upon held charge amount, have recently become widely known. A multivalued memory technique, in which information of two bits or more is stored by setting a plurality of charge amount thresholds, is also developed.
In such semiconductor memories, the charges are discharged with the elapse of time. Accordingly, upon the discharge of the charges in an amount beyond the threshold, an error occurs in reading information. In particular, multivalued memories are generally narrow in threshold intervals and thus are highly likely to cause errors.
An error correcting mechanism for correct restoration of erroneous information is provided in some storage devices using the semiconductor memory (see, for example, JP-A 2007-87464 (KOKAI)).
The error correcting mechanism, however, cannot properly correct an error when the error is beyond the error correcting capability. When the error correcting mechanism corrects the error without the recognition that the error is beyond the error correcting capability, a further error is disadvantageously added.